It is known to provide a screwdriver bit and finder combination for attachment to power tools such as power screwdrivers. In one example of a conventional bit and finder, a bit is manufactured of hexagonal steel stock with the blade for driving a slotted-head fastener formed at one end, and an annular recess for engagement by the power screwdriver formed at the other end. The width of the blade is the same as the diameter of the bit. A cylindrical finder having an inside diameter considerably larger than the diameter of the bit is mounted on the bit shank. A coil spring is mounted over the bit between the shank and the inside surface of the finder. The spring is connected at one end to the bit shank and is trapped at its other end against a ledge formed on the inside surface of the finder.
The driving end of the finder is designed to "find" or locate slotted-head fasteners over a broad range of fastener head diameters. Also, the blade is formed with a chisel edge. In use, the operator pulls the finder back to expose the blade with one hand and then inserts the bit with the other hand into the screw recess. The operator then allows the finder to spring back to cover the head of the screw.
One of the inherent disadvantages of this conventional structure is that the large amount of clearance between the bit and the inside diameter of the finder permits the bit blade to wobble in two directions, both in a direction in the same plane as the blade, and from side to side in a direction transverse to the blade. This wobble means that the blade initially encounters the fastener head along an axis that is misaligned, or at an angle, to the axis of the fastener head. The result (as has been experienced by most users of screwdrivers), is that the blade contacts the fastener recess at an end point of the chisel, rather than along the entire edge or side face of the blade, mulilating the bit, the fastener or both.
This effect is magnified when the user attempts to drive a fastener that is accommodated by a "one size fits all" finder which in reality is much too large for the bit. In this situation, not only would the "wobble" effect occur, but, when a small bit, for example, a #6 bit, is used to drive a larger fastener (for example, a #8), there is far too little blade drive surface in engagement with the fastener head slot. Also, in view of the wobble effect, it is likely that the bit will engage the fastener recess at an angle to the fastener axis, when viewed in the plane of the blade. The mismatch of the blade width relative to the slot diameter of the fastener means that much more force must be exerted by the user to drive the fastener into a workpiece. This is analogous to a person who pushes a door at its center rather than near the knob, finding it much harder to open.
A converse mismatch occurs when, for example, the user desires to drive a #6 fastener with a #4 bit. The wobble effect increases the likelihood that the blade of the bit will be off-center or not fit the fastener recess, a condition which once again yields poor driving performance.
Accordingly, it can be seen that with this conventional bit and finder, the desire to accommodate fasteners having large ranges of head diameters with a single bit size is purchased at the cost of poor fastener driving performance, wasted time and mutilated bits and fasteners.